Italy warned that the European Union must keep its doors open to eventual membership for Western Balkan countries.
The day before Trump met with Putin, he acknowledged the possibility of Russian interference in the election, but said other countries could have been responsible as well.
President Donald Trump is breaking with tradition by visiting Poland, an ex-communist country in central Europe, before making a presidential visit to longtime allies Britain, France or Germany.
Moscow has only once before suspended the hotline, which was established in October 2015 to prevent conflict between the different forces operating in Syrian airspace.
Serbia has formed an international legal team to file a lawsuit against NATO over its alleged use of depleted uranium munitions/